Raman spectra for a natural water sample have been comprehensively investigated as a function of temperature and salinity, and we demonstrate that temperature and salinity can be determined from Raman spectra with RMS errors consistently below ±0.2 °C and ±0.6 PSU respectively where there is variation only in one parameter. Most significantly, we have applied multivariate methods to show that both temperature and salinity can be determined simultaneously from Raman spectra with RMS errors of ±0.7 °C and ±1.4 PSU respectively, and designed a three-channel Raman spectrometer that will be used for future studies.